Heater element for electron discharge devices



24, was. v. 0. ALLEN 29% pw HEATER ELEMENT FOR ELECTRON DISCHARGE DEVICES Filed April 12, 1930 Patented Mar. 24, 1936 UNITED STATES PATENT OFFICE HEATER ELEMENT FOR ELECTRON DISCHARGE DEVICES Application April 12, 1930, Serial No. 443,693

4 Claims.

This invention relates to heater elements and with particularity to methods and means for heating the electron motors such as used in audions and space discharge devices generally.

The invention has for its principal object to provide a novel methodof heating an electron emissive member to render it electronically active.

In certain types of space discharge devices such as audions or the like, it is desirable to employ an electron emitting surface of relatively large area. This is particularly true in such devices as rectifiers, or the like. Furthermore, it is Hequently desirable to be able to heat the electron emitter by an alternating or pulsating current Without causing the alterations of the heating current to be reproduced from the output circuit of the device. As a solution for both of these problems it has been proposed to employ a heater filament which passes through and is supported by a relatively large insulating block or rod. Inasmuch as the heater filament when in operation is at a relatively high temperature and since the insulating member must necessarily be subjected to heavy strains due to the heating up of the filament practical reasons require that the insulator be made of comparatively greater mass than the heating filament itself. Thus in one known type of heater for electron discharge devices the heater element is in the form of a hairpin filament which passes through a pair of iongitudinal bores in a, cylindrical insulator. It has been found, however, that in order to provide the necessary rigidity of construction that the insulating rod must be made of a certain minimum cross-section. As a result of this enforced limitation as to the minimum size of the insulator the heater element, as a whole, exhibits a considerable time lag between the application of heating current to the filament and the passage of a signal or the eifective emission of electrons from the emitting member.

Various attempts have heretofore been made to reduce this time lag in socalled indirectly heated cathodes. For example, in one type the filament is spaced entirely freely throughout its length from the walls of the electron emitting cathode. While this type of heater may possess desirable characteristics from the viewpoint of rapidity of response, nevertheless it possesses great disadvantages both from the manufacturing viewpoint and from the actual operating viewpoint.

It is, therefore, another object of the present invention to provide a. method of mounting and supporting a heater element with relation to an electron emitting surface so that the desired rigidity of the heater element as a whole is obtained and, at the same time, the device possesses a minimum time lag.

Another feature of the invention is to provide 5 a method of heating an electron emitting surface simultaneously by conducted heat .as well as by directly radiated heat from a heating element.

Another feature of the invention relates to an 10 electron emitting member of the indirectly heated type wherein the heater element is exposed at spaced intervals to the electron emitting surface.

Another feature of the invention relates to an indirectly heated cathode employing a fila- 15 mentary heating element together with means for freely spacing the filament from the heating surface at spaced intervals.

Another feature of the invention relates to what may be termed a skeleton like insulator rod for supporting a heater filament in an indirectly heated cathode.

A further feature relates to the method of manufacturing the skeleton like insulators according to the invention. 5

A further feature relates to an indirectly heated cathode which has a maximum rigidity free from accidental short circuitings between the heating filament and the cathode surface and, at the same time, possesses a minimum of time lag.

A still further feature relates to the organization, arrangement and relative location of parts which go to make up an electron emitting cathode of the indirectly heated type.

Other features and advantages of the invention not specifically enumerated will be apparent after a consideration of the following detailed descriptions and the appended claims.

In the drawing- Figure 1 represents a conventional and known type of insulator rod as now used in electron discharge devices. This figure also illustrates schematically the method of removing portions of the rod to produce its mass;

Fig. 2 is a side view of the rod of Fig. 1 after portions of the wall thereof have been removed;

Fig. 3 is another View of the rod shown in Fig. 2 also showing the manner in which the heater filament is supported by the insulator;

Fig. 4 shows an electron emitting cathode employing the heater element shown in Fig. 3;

Fig. 5 is a sectional view of a modified form of insulator according to the invention;

Fig. 6 is a top plan view of the device shown in tour.

Fig. 7 shows another manner of supporting the filament on the insulator member of Figs. 5 and 6.

Referring more particularly to Fig. l the numeral I represents a rod of any suitable insulating material such as is ordinarily employed in the construction of indirectly heated cathodes for audions or the like. Preferably, the rod I is made of refractory insulating material and is also preferably, although not necessarily, circular in crosssection; Rod I as shown in the drawing is provided with a pair of longitudinal bores 2, 3, through which the heater filament is adapted to be threaded. It is obvious that in devices of this character it is absolutely necessary that the rod I possess the requisite strength or rigidity, both because of the temperature changes to which it is subjected in actual use and, furthermore, the size of the rod is material determined by the fact that the bores 2 have to be provided therein. As the result of these two limiting conditions a certain minimum cross-section of rod has heretofore been employed and with this minimum size rod there exists an undesirable heat inertia when heat is imparted to the rod.

To reduce this heat inertia without at the same time reducing the mechanical strength, insulating and spacing functions of the rod l the present invention contemplates the notching, cutting away, recessing or in any other manner rendering either one or both sides of rod l irregular in con- Thus, as indicated by the dotted lines in Fig. 1, the opposite faces of rod l are cut away to form circular depressions or notches therein which notches are staggered on the opposite faces of the rod. The manner of removing the material from the rod may be accomplished in any suitable fashion. However, with one type of insulating material it has been found that the depressions may be accurately and economically produced by sand blasting or similar operation.

Fig. 2 shows a side view of the rod of Fig. 1 with the portions of the wall thereof removed as above described, thus providing a series of notches for depressions 4 in the face of the rod. While any 7 quantity of material may be removed from the rod I with corresponding degrees in the heat inertiathereof it is preferred to cut the rod to such a depth as to expose the bores in the rod as indicated by the numeral 5 in Fig. 2. It will be seen,

therefore, that there is thus provided what may be termed a skeleton like insulator which, however, possesses in general a circular periphery and is capable of receiving and supporting the usual cathode sleeve without modifying the usual or present assembly operations.

Fig. 3 shows another view of the rod I with the heater filament 6 passing therethrough.

As will be evident from an inspection of this figure the filament'is exposed at spaced intervals throughout its length as indicated by the numeral 1. Consequently when the rod I is su'rroundcd'by a metal sleeve or the like, said sleeve is heated simultaneously by heat conduction through the solid portions 8 of the rod body and also is heated by direct radiation from the exposed portions 1 of the filament.

Thus there is shown in Fig. 4 a typical form of indirectly heated cathode comprising a notched or corrugated rod l similar to the rod of Figs. 2 and 3, said rod being surrounded throughout its length by a suitablemetal sleeve 9 the exterior surface of which is covered with an electron emissive coating ID in any well known manner. Due to the general circular periphery of the rod I the sleeve 9 can be assembled snugly thereover and at the same time the heater filament is positively prevented from short circuiting with said metal sleeve. Furthermore, since the sleeve is exposed at spaced intervals to the direct radiation of heat upon the filament the sleeve heats up extremely rapidly and actual devices have been constructed with a time lag of not more than six seconds. Furthermore, it has been found that the cutting away of the surface of the insulator rod does not materially decrease its mechanical strength so far as changes in temperature are concerned.

While in the foregoing there has been described a rod of general circular periphery it will be understood that the invention is not limited thereto but that any other type of rod may be employed. Thus there is shown in Figs. 5 and 6 an insulator rod II which has flat side faces I2 and rounded ends I3. The ends I3 are undercut or notched as indicated by the numeral M in the manner. described in connection with Figs. 1 to 4. Due to the shape of the rounded ends l3 the rod may be easily and snugly fitted with the usual cathode sleeve l5.

It will be seen, therefore, that the electron emitter shown in Figs. 5 and 6 possesses an optimum of mechanical rigidity, a minimum of heat inertia and without increasing the liability to short circuits between the heater filament and the cathode sleeve.

It will be understood that the drawing is intended to be merely illustrative of two preferred methods of carrying out the invention and that any equivalent manner of heating the cathode sleeve simultaneously by conducted heat and radiated heat constitutes the broad feature of the invention. Furthermore, while the heater filament and insulator rod are shown as mounted within a sleeve itwillbe understood that any other depression of the emitting surface and the heater element may be employed.

Furthermore, while one preferred method of making the rod has been described other equivalent methods may be employed. For example, instead of making the rod of a certain outside diameter and then undercutting the rod it will be obvious that a rod of a certain diameter may be provided with staggered projections attached thereto orformed thereon in any other manner. Furthermore, the rod instead of being cut or notched maybe molded or cast into the shape shown in Figs. 3 and 5. Likewise, instead of notching two sides of the rod I or more than two, two faces may be notched. Furthermore, instead of employing the hairpin like filament any other type of heater wire may be employed.

Fig. 7 shows how the filament can be mounted in the insulator rod without threading it entirely through the length thereof, thus enabling the same insulator rod to be used for different heater characteristics as desired.

What I claim is:

1. A heater element comprising an insulated core having. a plurality of staggered projections, a heater wire passing through said core, and having alternate parts only of its length exposed between adjacent projections. r r

2. An insulator member for electron discharge devices comprising a rod of insulating material having a pair of bores extending longitudinally therethrough, the opposite sides of said rod being provided with spaced notches, the notches on one side being staggered relatively to the notches on the other side.

3. An insulator member according to claim 2 7 in which the notches are undercut relatively to the bores, whereby a heater wire passing through said bores is exposed at spaced .points throughout its length.

4. An insulator member for electron discharge heaters comprising a rod of insulating material,

having a plurality of staggered lateral projections on opposite sides intermediate its ends, said projections being provided with perforations to receive and support a heater wire passing therethrough.

VICTOR O. ALLEN. 

